1. Field of the Invention
The present invention relates to a high-frequency magnetic head suited for use in recording and reproducing high-frequency signals which are generally employed in high-quality VTR, digital VTR or the like.
2. Description of the Prior Art
Development of ring-type magnetic heads is being pursued by the use of metallic magnetic material such as, for example, sendust or an amorphous alloy. The high-frequency magnetic heads can be obtained by reducing the loss of eddy currents in a high-frequency region of a magnetic core made of the metallic magnetic material. To this end, the magnetic core has a metallic magnetic film of a laminated structure in which metallic magnetic thin layers and insulating layers are alternately laminated one upon another.
It is preferred that the metallic magnetic film of the ring-type magnetic head is an isotropic film having a small anisotropy. In applications where the amorphous alloy is employed as the metallic magnetic material, magnetic anisotropy is generally induced therein in the presence of a magnetic field. It is, therefore, necessary to make the metallic magnetic film isotropic by reducing the magnitude of the induced magnetic anisotropy during the manufacture of the magnetic head. Accordingly, a heat treatment required for the manufacture of the magnetic head is generally carried out in a rotating magnetic field at a temperature of less than a crystallization temperature Tx where formation of a Co-containing magnetically soft film having composition of the crystallization temperature Tx less than the Curie temperature Tc is desired, and in the absence of any applied magnetic field at a temperature of from Tc to Tx where formation of a Co-containing magnetically soft film having composition of a crystallization temperature Tx greater than Tc is desired, thereby dispersing the anisotropy.
However, because such an isotropic Co-containing magnetically soft film has relatively small local anisotropic magnetic fields, the initial permeability in a high-frequency region (for example, over 30 MHz) is deteriorated by the action of natural resonance. Even if the thickness of each of the layers of the laminated film is made thin, the initial permeability is not improved in the high-frequency region and, hence, has a limit in this region. Because of this, the problem arises that the magnetic head has a limit in high-frequency characteristics, and the present condition is that conventional magnetic heads cannot satisfy requirements of, for example, a high-quality digital VTR system in which the high-frequency characteristics are required in the range of not less than 30 MHz.